Solar photovoltaic (PV) and solar photothermal (PT) systems can meet global electrical energy needs. However, due to solar energy's low power density, megawatt to gigawatt scale PV/PT plants require a large area for installations and are best suited for semi-arid and desert regions. These areas are the sunniest but also the dustiest locations in the world. Deposited dust strongly adheres to solar panels and solar concentrators and obscures the solar radiation reaching the PV cells and mirrors, reducing energy conversion significantly. Deposition of only four grams of dust (with particle size in the range from 0.5 to 10 μm in diameter) per square meter on a panel may reduce power output by 40%.
U.S. Pat. No. 6,911,593 of Mazumder et al. describes an electrodynamic shield embedded within a thin transparent dielectric film or a sheet used to remove dust deposited on solar panels.
Some of the major difficulties in applying EDS on solar panels include (1) avoiding interactions between the electric field of the EDS electrodes and current collecting grids used in solar panels for providing electrical power, (2) scaling of the method of EDS construction for manufacturing and installing transparent electrodes on solar panels and solar concentrators, (3) obscuration of solar radiation caused by the placement of the EDS on the surface of solar panels and concentrators, (4) retrofitting existing solar photovoltaic and photothermal devices with self-cleaning EDS systems, (5) environmental degradation of polymer films under outdoors condition, (6) maintaining the efficiency of heat dissipation of solar panels integrated with EDS, and (7) cost-effective manufacturing of new solar panels and solar concentrators integrated with electrodynamic screens for large-scale installations.
Efforts to maintain solar panels and solar concentrators clean have been investigated by a number of researchers. However, the current methods are limited to manual cleaning of solar collectors with water and detergents. A soft brush with a long handle is generally used. Some reported technologies on self-cleaning glass involve passive surface treatment methods to modify the front surface to be either highly hydrophilic or highly hydrophobic.
One commercial product available for building applications is the hydrophilic self-cleaning glass coated with a thin layer of photoactive crystalline titanium dioxide (TiO2) particles. When UV radiation is incident on the TiO2 coated glass, the surface becomes highly hydrophilic and its moisture absorbing capacity increases substantially. When the surface is cleaned with water or is exposed to rainfall, the wetting characteristics of the glass plate help the surface to be easily cleaned. Deposited dust can be washed away due to the super hydrophilic property of the glass. However, the process has major limitations: (1) there is high reflection loss of sunlight since the refractive index of TiO2 is higher than that of the glass, (2) water (or rain) is needed to remove the dust, and (2) presence of UV radiation (wavelength shorter than 380 nm) is needed to activate the surface. In semi-arid and desert areas water is scarce and rainfall is infrequent.
Application of highly hydrophobic surface has also been reported for minimizing adhesion of dust on glass plates. Super hydrophobic transparent films or plates based on nanostructured properties have very low surface energy, which minimizes van der Waal and capillary adhesion forces between the dust particles and the glass surface. The electrostatic forces of adhesion are not decreased. When exposed to outdoor conditions the hydrophobic properties of the surface are adversely affected by UV radiation and dust deposition, limiting the durability of super hydrophobic surface less than a few months.
Methods involving mechanical cleaning of panel surfaces by applying vibration, using wipers, moving transparent films over the panel surface, and using water have also been reported. Applications of electrostatic and electromagnetic fields for controlling particle motion have also been published. However, these reports have tended not to address the development of manufacturing processes involved in the fabrication and installations of electrodynamic screens (EDS) on solar panels and solar concentrators (mirrors and lenses) for removing dust and providing self-cleaning properties of solar photovoltaic (PV) and solar photothermal (PT) systems.